In recent years, from a perspective of preserving the environment, it is becoming popular to use a power generating apparatus of a renewable energy type such as a wind turbine generator utilizing wind power and a renewable energy type turbine generator such as a tidal current generator utilizing tidal. In the power generating apparatus of the renewable energy type, a motion energy of the wind, the tidal current, the ocean current or the river current is converted into the rotation energy of the rotor and the rotation energy of the rotor is converted into electric power by the generator.
In the power generating apparatus of renewable energy type, a rotation speed of the rotor is small in comparison to a rated rotation speed of the generator and thus, a mechanical gearbox is usually provided between the rotor and the generator. By this, the rotation speed of the rotor is increased to the rated rotation speed of the generator before being inputted to the generator.
Between the gearbox and the generator, a braking mechanism (a brake disc and a brake caliper) is also provided. The braking mechanism is provided to brake the rotor and to maintain the rotor in a stopped state. Herein, the brake disc is provided between the gearbox and the generator as a rotation shaft (an output shaft of the gearbox and an input shaft of the generator), which rotates at high speed between the gearbox, and the generator has lower torque, e.g. 1/100 than a rotation shaft (the main shaft) on an upstream side of the gearbox.
Disclosed in Patent Literature 1 (see FIG. 3), is a technology to store a brake disc and a brake caliper inside a casing of the generator.
In recent years, efforts have been made to develop a power generating apparatus of renewable energy type which uses a hydraulic transmission combining a hydraulic pump and a hydraulic motor, instead of the gearbox which is an obstacle to reduce weight and cost of the apparatus.
Although not related to the braking mechanism, disclosed in Patent Literature 4, is a turning device which rotates a main shaft by a hydraulic cylinder via an adapter disc mounted to a strain washer connecting a main shaft and a gearbox of a wind turbine generator. This type of turning device is used for rotating the rotor to a desired angle when attaching and detaching of the blade or the like.